String content and var style updates

[Steven Gagniere (sgagniere)]

Checklist

1. [CRUCIAL] Is the change for CP or CCloud functionalities that are already live in prod?
   • yes: ok

What

Various changes to strings in internal/pkg/errors/strings.go and internal/pkg/errors/error_message.go (and affected files):

• Typo fixes.
• Changed (most) error messages to follow guidelines: first word not capitalized (unless it's a proper noun) and no full-stops at the end.
• Changed (most) suggestion messages to follow guidelines: first word capitalized and a full stop at the end of each sentence.
• Removed unused strings.
• Removed newline characters at the end of the last sentence of some suggestions.
• Added a space between the end of a url and the fullstop in some suggestions to avoid possible confusion about whether or not the fullstop is part of the url.
• Updated README to reflect these last two styles.
• Added ErrorMsg suffix to some error string variables which were missing it, and modified the suffix of some strings being used as error messages from Msg to ErrorMsg.
• Changed the suffix of some suggestions from Suggestion to Suggestions to match the README guidelines (even when the suggestion consists of a single sentence).
• Moved a Msg from error_messages.go to strings.go.

References

N/A

Test & Review

Ran make test.

[David Hyde (DABH)]

Looks good, thanks for the cleanup! ✨

[David Hyde (DABH)]

Why did this one lose a period but the one below gained a period? (Conservation laws aside...)

[Steven Gagniere (sgagniere)]

This one's an error, so it doesn't have an ending period. The next one (assuming it's describe-invalid-role-cloud.golden is a suggestion, so I added one.